One of the most delicate phases during PTCA is the passing of a guide-wire tip through the targeted lesions (stenosis). The vessel walls at this location are usually uneven and, by definition, the conduct is narrowed. It follows that stenosis passing is one of the most time consuming (and therefore dose generating) parts of the intervention.
One of the reasons why the stenosis passing phase is difficult comes from the fact that it is achieved almost blindly and on a moving target. Most of the time, the physicist only sees the wire tip while trying to figure out what the stenosis looks like and what is the exact location of the tip within that stenosis. In this process, the physicist may either try to mentally register the current tips location with the stenosis visible in the angiogram, or he may inject a small shot of contrast agent.
A first approach that consists in comparing with the angiogram is difficult and bound to all sorts of inaccuracies, in particular due to the cardiac and respiratory motions.
A second approach that involves contrast agent injection is unfortunately very transitory and only offers a glimpse of the situation. It is also made difficult by the cardiac and respiratory motions.
A third solution would consist in using some kind of cardiac road mapping technique. This kind of solution does not yet exist on current intervention systems and is difficult to implement.
A description of a basic interventional procedure can be found in ‘Algorithmic Solutions for Life Device—Two-Vessel Match’, J. Bredno, B. Martin-Leung, K. Eck, in the proceedings of SPIE, Volume 5370-Medical Imaging 2004: Imaging Processing, J. Michael Fitzpatrick, Milan Sonka, Editors, May 2004, Pages 1486-1497. Accordingly, after a catheter is inserted into the vascular system at an access site, it is advanced along large vessels to the vascular structure that requires treatment. Contrast agent is injected via the catheter and cathlab X-ray equipment records an angiographic sequence that shows the vessels when filled with contrast agent. The diagnostic angiogram acquisitions can be repeated with varying imager geometries. Diagnosis and intervention planning are based on such diagnostic angiograms. During intervention, a flexible, partially or fully radial opaque guide-wire is advanced to the affected vascular structures, e.g. stenosis in coronaries, neurovascular aneurysms, or arterio-venous malformations. Fluoroscopic low-dose X-ray surveillance visualizes the guide-wire and allows for the hand-eye coordination of the interventionalist while advancing the guide-wire. When positioned, the guide-wire serves as rail to deliver interventional devices, e.g. balloons for dilation and stent delivery, detachable coils for aneurysm clotting. The delivery and deployment of the interventional devices is also fluoroscopic controlled.